Rheological Evaluation of Dense Suspensions: Simulation of a Fresh Cement Paste

Summary The rheology of fresh cement pastes is a function of not only particle size, shape, and concentration, but also the cement setting reactions. This greatly complicates the analysis of data obtained in any rheological experiment. To separate the slurry contribution to the system rheology from the chemical reaction component, a slurry of marble-dust particles is used to represent a cement slurry. In this study, both tube-flow and concentric-cylinder [Rheometrics Pressure Rheometer™ (RPR)] rheometers are used to evaluate the rheological behavior of the dense suspensions. The apparent "slip" of the suspension makes correlation of the flow curves generated from the two viscometers difficult. The degree of slip in both viscometers becomes increasingly significant as the marble-dust concentration increases. The use of a grooved bob in the concentric-cylinder viscometer considerably reduces the amount of slip. Large annular gaps can also contribute to inconsistent results. An analysis of the data from both types of viscometers is presented. The Reiner-Riwlin equation, derived for a Bingham fluid, was used to approximate the flow curves generated with the concentric-cylinder viscometer. Marble-dust suspensions displayed antithixotropic behavior regardless of the water/solids ratio tested. These data are representative of an antithixotropic system that builds structure as the shear rate is increased. The duration of the tests affects the observed data only when sedimentation occurs during the test. When the denser marble-dust suspensions are tested, sedimentation occurs in the viscometer, producing an irregular shear thinning. Marble-dust suspensions generally provide a good model system for gaining an understanding of the rheological properties of fresh cement pastes.